At long last, it's been scientifically, mathematically, and economically proven: Women are kinda bummed out. And not just since the unemployment rate started creeping toward 10 percent; we have been sinking into this funk for the past 35 years.

According to a perplexing new study from the University of Pennsylvania's Wharton School, women have experienced a steady erosion in happiness since the early 1970s, such that, while we used to test as happier than men, we are now notably less stoked than the hairier sex. The finding holds across many different polls and no matter how you slice the data—whether you are married, single, teenaged, elderly, rich or poor, American or European, a single mother or a child-free career gal—if you have two X chromosomes you are, statistically speaking, probably less happy than the dudes you know (who have become slightly more happy than they used to be, though still not as happy as women were in 1972).

When I read the study over the dank, rainy, recessiony summer, I wasn't exactly surprised to discover that women are eking less satisfaction out of life than men: It's well known that women report higher levels of depression and take the lion's share of antidepressants. The shocker was that the authors, economists Betsey Stevenson and Justin Wolfers, offered no smoking gun to explain women's doldrums. Not only that but their data shot down a lot of the old scapegoats we've been flogging for years—working mothers, single mothers, divorce, the second shift of housework after paid work.

"It's a blank slate," Stevenson said when I spoke to her recently. "You can project onto it anything you want." How intriguing! What fun! Happy days are here again! Let the projecting commence!

"The Long, Slow Disappointment"
The current vogue for genetic determinism— the idea that we are born with certain set points and predilections and that no amount of cajoling, dieting, or lottery winning will ever make us thinner, happier, or more successful than our genes dictate— has us all in the mind-set that biology is destiny. But a downshift in set points like this one would take a millennium to occur genetically. Besides, when it comes to mental health, heredity isn't quite as powerful as most people believe. Epidemiological studies on twins show it accounts for about 50 percent of our relative happiness, with the other half made up of our circumstances and choices (the two of which are, of course, intertwined).

Susan Krauss Whitbourne, professor of psychology at the University of Massachusetts and author of next month's The Search for Fulfillment, recently completed a 40-year study of how personality developed in a group of baby boomers. According to her findings and extrapolating thereof, her subjects were very much influenced by the prevailing social and political winds. In the antiestablishment '60s, her sample was much less industrious, for example, and in the selfish, status-obsessed '80s, everybody abandoned community service and their happiness suffered.

When I spoke to Stevenson this fall, she and Wolfers (her partner in life as well as in economics) were on family leave, having just had their first child, a daughter. Stevenson was born in the early '70s and she hypothesizes that, as with Whitbourne's boomers, our place in time may be somewhat to blame for our dip in happiness. It was in 1972 that Helen Reddy started singing "I am woman, hear me roar," right around the apex of hope and excitement in the women's movement. Women born into that era like Stevenson (and I) were fed a steady diet of girl power—having it all was our birthright. She remembers her dismay as a child when the Equal Rights Amendment failed to pass and theorizes that the years since have been a "long, slow disappointment" for women who dreamed a utopia of equality was just around the corner.

While many have used Stevenson's work to blame the women's movement for removing us from the heaven of housewifery, she makes exactly the opposite argument: "It's not the women's movement that's made us unhappy but the failures of the women's movement." The wage gap persists (women currently make 80 cents to the male dollar), women have not achieved parity as power brokers in government or corporations (only 17 of our 100 senators are women and only 15 Fortune 500 companies are run by women), and we still can't get a woman elected president. While we've no doubt made great strides (17 senators is better than the two in 1972), "women's ability to tolerate sexism and unequal treatment may be declining over time," she says.

We're Being Tom Sawyered
One failure of feminism you hear a lot about is the so-called second shift, or the burden of housework and child care that working women face because men aren't doing their fair share. However, this turns out not to be totally true. Stevenson and Wolfers point to numerous studies showing that women's and men's total work hours (paid plus unpaid) have been declining since 1965—both sexes have more leisure time than in the past—and men are, in fact, doing more housework than ever before (though they still have a ways to go to catch up to the fairer sex).

If this doesn't seem to reflect what's going on in your home, the problem may be more qualitative than quantitative. While you and your husband may be logging about the same number of hours of work, some recent surveys show that he may be enjoying his more. In other words, men may be cherrypicking the good stuff and leaving the "shit work" to women, who are supposed to be grateful for the opportunities in the office and the help at home. "It's a controversy in research, deciding if an activity is leisure or work," Stevenson says. Child care, for example, can be a blast or a drag, depending on what kind of care the kid needs and your frame of reference: "When my mother takes care of my daughter, it's leisure, not work," Stevenson points out. "But I have to pay my nanny to do the same thing."

"The Paradox of Choice"
Another theory is that while the women's movement opened up possibilities, it also opened our eyes to new ways we might fail. Liberation is like original sin you realize you're powerful but also naked and vulnerable, and that snake in the next cubicle isn't as nice as you thought he was. "It's the paradox of choice," says Sonja Lyubomirsky, professor of psychology at the University of California and author of The How of Happiness. "It increases your chances for happiness but also regret."

While much ink has been spilled on how women with multiple roles in life—wife, mother, executive, church leader—are more resilient in the face of adversity (if something goes wrong at home, hey, you can still feel good about your performance at work, the reasoning goes), all this variety may be giving women more arenas to find themselves lacking. Susan Nolen-Hoeksema, PhD, professor of psychology at Yale University and the author of next month's The Power of Women, says that multitasking is a boon only if you like what you're doing: Women earning crappy pay in a crappy job who go home to crappy husbands who treat them like crap are not getting the same thing out of their multiple roles that, say, Nancy Pelosi might be.

The Power to Complain
One thing is certain: Progress has given us the license to moan and groan about our crappy jobs and husbands (and a spiffy new form of media, the blog, tailor made to such ranting!). And this, says Stevenson, further complicates studies on well-being over time. "It's possible that in the era of the feminine mystique, women felt ashamed to admit they weren't happy," she says. "We might find that women haven't changed their happiness levels; what's changed is the social sanction for telling the truth."

Nolen-Hoeksema even conjectures that things may have swung too far in the other direction, so that now misery has become a badge of honor. "It becomes a oneupsmanship thing," she says. "The more completely stressed-out you are, the higher your status." While we've known for a long time that viruses and fashion fads can be contagious, a burgeoning field of research has begun to show that health factors such as obesity and depression may be catching too. It's possible, Nolen-Hoeksema says, that we could be abetting this spiral of unhappiness by giving it so much airtime. She actually wrote the book on how women tend to perseverate on the negative (Women Who Think Too Much), and her latest tome pushes women to focus on the good—the emotionally resilient, mentally flexible, socially intuitive, splendidly communicative, communitybuilding stuff about being a girl.

Stevenson also suggests the handwringing may be overkill. "Maybe being happy isn't the ultimate goal. Maybe things are good the way they are and we need to put less pressure on ourselves to be happy. Maybe what we want is to be dog tired at the end of the day but think, I'm really happy I have this career even though it doesn't leave a lot of time for yoga."

People Who Need People
When Whitbourne was evaluating her baby boomer subjects in their later years, she started focusing more on their "ego integrity"— which is a rough equivalent of fulfillment or happiness. The participants with high scores in that area were involved in activities that got them "outside themselves": volunteering, getting involved in the education of the next generation, etc. Healthy maturity, she writes, necessitates "a social interest that extended beyond [one's] own personal concerns."

Fulfillment, as the group approached their golden years, didn't require that they were always bubbling with joy—to the contrary, some of the most impressive instances of growth were in subjects who experienced tragedy and managed to go on. (Call it the Elizabeth Edwards effect—what didn't kill them made them incredibly admirable.) Fulfillment correlated with the feeling, Whitbourne writes, that "what you are doing in life is making a difference for others," particularly those who'll come after you. In other words, if you want to be happy, you've got to get off your couch and make someone else happy.